10 Everyday Things You're Probably Doing the Hard Way

Figuring out how much to leave for a restaurant tip was a little more difficult for some of us before there were apps to calculate it. There are several ways to calculate a tip in your head, though, and they aren't difficult -- this method will work no matter what (some calculations are based on the tax, but some states don't charge tax so those methods aren't foolproof).

Here's what you're aiming for: Tip your waiter or waitress 15 percent of the pre-tax bill (and as much as 20 percent for excellent service) [source: The Emily Post Institute]. Despite how many of us have trouble with this, one of the best ways to figure out that 15 percent in your head is no more than a two-step process.

First, calculate one percent of the bill. Let's use a $24.00 bill as our example: One percent of a $24.00 bill is $0.24 (just move the decimal point two places to the left).

Next decide how much you'd like to tip. For a 15 percent tip, multiply $0.24 by 15, which equals a $3.60 tip. Twenty percent for great service? Multiply $0.24 by 20 for a $4.80 tip -- and so on for calculating 16, 17 or any other percent you'd like.

Author's Note: 10 Everyday Things You're Probably Doing the Hard Way

Thanks to this article, I am now an expert tipper. I used to use another method, which, to be honest I never really liked unless I was calculating 20 percent. It went like this: First I'd calculate 10 percent of the bill, divide that resulting number in half, add the two together and there it was, the tip amount. So for example 10 percent of a $24.00 bill is $2.40. Divide $2.40 in half to calculate five percent. Add $2.40 and $1.20 for $3.60, a 15 percent tip. Figuring a 20 percent tip takes only two steps. First calculate 10 percent of the bill and then double that number. So, 10 percent of $24.00 is $2.40. Double that number -- $4.80 -- for a 20 percent tip. I'm exhausted just explaining it.

Jaeggi, Susanne M.; Buschkuehl, Martin; Jonides, John; and Walkter J. Perrig. "Improving fluid intelligence with training on working memory." Proceedings of the National Academy of Sciences of the United States of America. 2008. (Oct. 26, 2012) http://www.pnas.org/content/early/2008/04/25/0801268105.full.pdf+html

Lake, Matt. "HOW IT WORKS; Detectors Can Find Just the Right Spot to Drive That Nail." The New York Times. 2001. (Oct. 26, 2012) http://www.nytimes.com/2001/04/12/technology/how-it-works-detectors-can-find-just-the-right-spot-to-drive-that-nail.html